Weekend-Engagement #264: What has shocked you about someone you know well and why?

For this week I bring you a story of sex and betrayal, just the way you porky readers like it! The “who” is simple, my sister-in-law...the what and why, well now comes the fun.
Let's say that in her youth she was always a bit of a libertine, but then again, we were all a bit libertine when we were young, weren't we? After a few years, she seemed to have put her head on straight and had even found a boyfriend, her first serious one. From the outside, at least, everything seemed rosy and blossoming, so much so that we all said how she had put her head on straight, had finally found a serious relationship, and we saw them as a well-matched couple.
Except that one day, out of the blue, after a couple of years of engagement, he called us to tell us that they had broken up, there was no love, etc., the usual things.

Except that one evening we go out for a drink together and out of curiosity I start digging into the end of the story and I am shocked by what she tells me! Basically, there had been multiple betrayals on her part: a flirtation lasting several months with a client at work, like sexual encounters in the locker room; once these hot encounters with the client were over, she plunged into a much older man she had met at the gym, married and with a pregnant wife... and here too, hot encounters in the gym, in the car and so on and so forth, this went on for almost a year; to top it all off, a threesome with a friend and a friend of the friend! All this in the two years she was together with the other poor cuckolded wretch!
I was truly stunned and speechless, I mean if you get to do those things, what do you stay together for?

Some random photos
Post in response to @galenkp Weekend-Engagement topics: WEEK264